Myoclonus-dystonia: clinical and genetic evaluation of a large cohort

BACKGROUND

Myoclonus-dystonia (M-D) is an autosomal dominant inherited movement disorder. Various mutations within the epsilon-sarcoglycan (SGCE) gene have been associated with M-D, but mutations are detected in only about 30% of patients. The lack of stringent clinical inclusion criteria and limitations of mutation screens by direct sequencing might explain this observation.

METHODS

Eighty-six M-D index patients from the Dutch national referral centre for M-D underwent neurological examination and were classified according to previously published criteria into definite, probable and possible M-D. Sequence analysis of the SGCE gene and screening for copy number variations were performed. In addition, screening was carried out for the 3 bp deletion in exon 5 of the DYT1 gene.

RESULTS

Based on clinical examination, 24 definite, 23 probable and 39 possible M-D patients were detected. Thirteen of the 86 M-D index patients carried a SGCE mutation: seven nonsense mutations, two splice site mutations, three missense mutations (two within one patient) and one multiexonic deletion. In the definite M-D group, 50% carried an SGCE mutation and one single patient in the probable group (4%). One possible M-D patient showed a 4 bp deletion in the DYT1 gene (c.934_937delAGAG).

CONCLUSIONS

Mutation carriers were mainly identified in the definite M-D group. However, in half of definite M-D cases, no mutation could be identified. Copy-number variations did not play a major role in the large cohort.

Distal myoclonus and late onset in a large Dutch family with myoclonus-dystonia

We report a large myoclonus-dystonia (M-D) pedigree with a two-base pair deletion in Exon 5 of the epsilon-sarcoglycan gene. Three individuals had onset after age 40 years. Distal myoclonus of the arms was present in all 20 symptomatic mutation carriers. These findings expand the known phenotype of M-D and require revision of the current diagnostic criteria. Five of 14 asymptomatic mutation carriers who inherited the mutation from their mother showed minimal axial dystonia, arguing against a maternal imprinting mechanism.

Serial analysis of gene expression in differentiated cultures of human epidermal keratinocytes

Keratinocyte gene expression was surveyed more comprehensively than before, by means of serial analysis of gene expression. A total of 25,694 tags derived from expressed mRNA, were analyzed in a model for normal differentiation and in a model where cultured keratinocytes were stimulated for a prolonged period of time with tumor necrosis factor-alpha, thus mimicking aberrant differentiation in the context of cutaneous inflammation. Serial analysis of gene expression revealed many transcripts derived from unknown genes and a large number of genes that are not known to be expressed in keratinocytes; furthermore, these data provide quantitative information about the relative abundance of transcripts, allowing the identification of differentially expressed genes. A major part of the identified transcripts accounted for genes involved in energy metabolism and protein synthesis. A large proportion of all transcripts (6%) corresponded to genes associated with terminal differentiation and barrier formation. Another highly expressed functional group of genes (2% of all transcripts) corresponded to proteins involved in host protection such as antimicrobial proteins and proteinase inhibitors. Three of these genes were not known to be expressed in keratinocytes, and some were upregulated after prolonged tumor necrosis factor-alpha exposure. Our data on expressed genes in keratinocytes are consistent with the known function of human epidermis, and provide a first step to generate a transcriptome of human keratinocytes.

Induction of SLPI (ALP/HUSI-I) in epidermal keratinocytes

Secretory leukocyte protease inhibitor (SLPI) is a small, cationic protein that is known to be constitutively expressed by several glandular epithelia. SLPI inhibits leukocyte-derived proteinases, has anti-HIV-1, antibacterial, and anti-fungal properties, and interferes with the induction of synthesis of proinflammatory mediators in monocytes and macrophages. We now report that at both the mRNA and the protein level, SLPI shows inducible expression in a nonglandular epithelium. A weak expression of SLPI was found in the stratum granulosum of adult normal human epidermis; however, in lesional psoriatic epidermis and in migrating keratinocytes of healing wounds, a strong cytoplasmic staining was seen in the suprabasal keratinocytes. Remarkably, in the dermis adjacent to SLPI-expressing keratinocytes, SLPI was found extracellularly associated with elastin fibers, whereas the dermis in normal skin was negative. In cell culture, SLPI was hardly expressed in monolayers of proliferating keratinocytes. Differentiating cultures with a phenotype of normal skin expressed low levels of SLPI, whereas cultures with a regenerative/psoriatic phenotype expressed high levels. Functional studies with recombinant SLPI indicated that its antibacterial spectrum and potency are distinct from other anti-microbial peptides such as lysozyme and defensins. In view of the multiple functions of SLPI and the inducibility, we propose that it acts as an important first line defence mechanism in cutaneous injury.

Differential effects of detergents on keratinocyte gene expression

We have studied the effect of various detergents on keratinocyte gene expression in vitro, using an anionic detergent (sodium dodecyl sulfate), a cationic detergent cetyltrimethylammoniumbromide (CTAB), and two nonionic detergents, Nonidet P-40 and Tween-20. We measured the effect of these detergents on direct cellular toxicity (lactate dehydrogenase release), on the expression of markers for normal differentiation (cytokeratin 1 and involucrin expression), and on disturbed keratinocyte differentiation (SKALP) by northern blot analysis. As reported in other studies, large differences were noted in direct cellular toxicity. In a culture model that mimics normal epidermal differentiation we found that low concentrations of sodium dodecyl sulfate could induce the expression of SKALP, a proteinase inhibitor that is not normally expressed in human epidermis but is found in hyperproliferative skin. Sodium dodecyl sulfate caused upregulation of involucrin and downregulation of cytokeratin 1 expression, which is associated with the hyperproliferative/inflammatory epidermal phenotype found in psoriasis, wound healing, and skin irritation. These changes were not induced after treatment of cultures with CTAB, Triton X-100, and Nonidet-P40. This effect appeared to be specific for the class of anionic detergents because sodium dodecyl benzene sulfonate and sodium laurate also induced SKALP expression. These in vitro findings showed only a partial correlation with the potential of different detergents to induce clinical, biophysical, and cell biologic changes in vivo in human skin. Both sodium dodecyl sulfate and CTAB were found to cause induction and upregulation of SKALP and involucrin at low doses following a 24 h patch test, whereas high concentrations of Triton X-100 did not. Sodium dodecyl sulfate induced higher rates of transepidermal water loss, whereas CTAB treated skin showed more signs of cellular toxicity. We conclude that the action of anionic detergents on epidermal keratinocytes is qualitatively different from the other detergents tested, which might have implications for in vitro toxicology studies that use cell biologic parameters as a read-out. We would hypothesize that detergents cause skin injury by several mechanisms that include direct cellular toxicity, disruption of barrier function, and detergent specific effects on cellular differentiation, as demonstrated here for sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, and sodium laurate.

Transcription factor C/EBPalpha: novel sites of expression and cloning of the human gene

We describe the characterization of recombinant clones for the human transcription factor CCAAT/enhancer binding protein alpha (hC/EBP alpha). The intronless hC/EBP alpha gene is almost 90% homologous to its rat and mouse counterparts. The gene copies of more distant species are less conserved, but the alignment reveals a striking homology in five regions, of which four may be involved in transactivation functions while the fifth concerns the carboxy-terminal bZip sequences (basic region and leucine zipper) mediating sequence specific DNA-binding. In addition to the usual expression sites, significant transcript levels were detected in the epidermal compartment of human skin and in rat aorta by northern analysis. The presence of hC/EBP alpha is further documented by immunohistochemical analysis of human skin biopsies and cultured keratinocytes showing the nuclear presence of the protein, notably in the suprabasal layers of the epidermis and in human keratinocytes induced to differentiate.

Constitutive and inducible expression of SKALP/elafin provides anti-elastase defense in human epithelia

Skin-derived antileukoproteinase (SKALP), also known as elafin, is a serine proteinase inhibitor first discovered in keratinocytes from hyperproliferative human epidermis. In addition to the proteinase inhibiting domain which is directed against polymorphonuclear leukocyte (PMN) derived enzymes such as elastase and proteinase 3, SKALP contains multiple transglutaminase (TGase) substrate domains which enable crosslinking to extracellular and cell envelope proteins. Here we show that SKALP is constitutively expressed in several epithelia that are continuously subjected to inflammatory stimuli, such as the oral cavity and the vagina where it co-localizes with type 1 TGase. All epithelia from sterile body cavities are negative for SKALP. In general, stratified squamous epithelia are positive, whereas pseudostratified epithelia, simple/glandular epithelia and normal epidermis are negative. SKALP was found in fetal tissues of the oral cavity from 17 wk gestation onwards where it continued to be expressed up to adult life. Remarkably, in fetal epidermis SKALP was found from week 28 onwards, but was downregulated to undetectable levels in neonatal skin within three months, suggesting a role during pregnancy in feto-maternal interactions or in the early maturation phase of the epidermis. Immunoelectron microscopy revealed the presence of SKALP in secretory vesicles including the lamellar granules. In culture models for epidermal keratinocytes we found that expression of the endogenous SKALP gene provided protection against cell detachment caused by purified elastase or activated PMNs. Addition of exogenous recombinant SKALP fully protected the keratinocytes against PMN-dependent detachment whereas superoxide dismutase and catalase were only marginally effective. These findings strongly suggest that the constitutive expression of SKALP in squamous epithelia, and the inducible expression in epidermis participate in the control of epithelial integrity, by inhibiting PMN derived proteinases.

Cell kinetic characterization of cultured human keratinocytes from normal and psoriatic individuals

Psoriasis is a chronic skin disease characterized by epidermal hyperproliferation, disturbed differentiation, and inflammation. It is still a matter of debate whether the pathogenesis of psoriasis is based on immunological mechanisms, on defective growth control mechanisms, or possibly on a combination of both. Several in vivo cell biological differences between psoriatic lesional epidermis and normal epidermis have been reported. However, it is not clear whether these changes are causal or consequential. In case that keratinocytes from psoriatic patients have genetically determined deficiencies or polymorphisms with respect to autocrine growth regulation and the response to inflammatory cytokines, we hypothesize that these differences should be maintained in culture. Here we have started a systematic comparison of first passage keratinocytes cultured from normal skin and uninvolved psoriatic skin to address the question whether there are intrinsic differences in basic cell cycle parameters. In an established, defined culture system using keratinocyte growth medium (KGM) we have determined: (i) cell cycle parameters of exponentially growing keratinocytes, (ii) induction of quiescence by transforming growth factor beta 1 (TGF-beta 1) and (iii) restimulation from the G0-phase of the cell cycle. Bivariate analysis of lodo-deoxyuridine incorporation and relative DNA content was performed by flow cytometry. Within the limitations of this model no gross differences were found between normal and psoriatic keratinocytes with respect to S-phase duration (Ts), total cell cycle duration (Tc), responsiveness to TGF-beta 1 and the kinetics for recruitment from G0. In psoriatic keratinocytes we found a lower amount of cell in S-phase and a shorter duration of G1, compared to normal keratinocytes. The methodology developed here provides us with a model for further studies on differences between normal and psoriatic keratinocytes in their response to immunological and inflammatory mediators.

Cell kinetic characterization of growth arrest in cultured human keratinocytes

In this study we have performed a cell kinetic characterization of growth and growth arrest of keratinocytes derived from normal human skin. Proliferative activity of the cell cultures was analysed with a flow cytometric technique, measuring relative DNA content and iododeoxyuridine (IdUrd) incorporation simultaneously. Normal human keratinocytes were grown in keratinocyte growth medium (KGM) and growth arrest was induced by using either keratinocyte basal medium (KBM) or KGM supplemented with TGF-beta 1. It was found that human keratinocytes grown in KGM plus TGF-beta 1 were growth-arrested within 52 hours. The rate of IdUrd incorporation into DNA decreased by more than 95% after 52 hours and paralleled the decrease of cells in S-phase. Within 52 hours after addition of TGF-beta 1, 79% of the growth-arrested cells were in the G0/G1-phase of the cell cycle, a situation that approaches that of the normal epidermis. Growth arrest of human keratinocytes in KBM showed a similar decrease in the rate of IdUrd incorporation. However, the decrease in IdUrd incorporation was not reflected in a decrease in cells in S-phase, suggesting that the cells were blocked in G0/G1, S or G2/M-phase rather than selectively in the physiological growth arrest state of G0/G1. Secondly, we investigated the kinetics of the cells when they were restimulated after growth arrest. We found that after termination of the growth arrest in KGM supplemented with TGF-beta 1 the cells require 6 to 8 hours to initiate DNA synthesis, with a continued decrease in the G0/G1 population, suggesting that the cells are recruited as a cohort. After growth arrest induced by KBM, cells also require 6 to 8 hours in KGM to initiate DNA synthesis, but the cells are not recruited as a cohort. We conclude that growth arrest induced by TGF-beta 1 is the preferred system in which to study induction of keratinocyte proliferation, since it induces a state of quiescence that approaches that of normal human epidermis.

Long-range physical maps of two loci (Aps-1 and GP79) flanking the root-knot nematode resistance gene (Mi) near the centromere of tomato chromosome 6

The root knot nematode resistance gene Mi in tomato has been mapped in the pericentromeric region of chromosome 6. With the objective of isolating Mi through a map-based cloning approach, we have previously identified and ordered into a high-resolution genetic linkage map a variety of tightly linked molecular markers. Using pulsed-field gelelectrophoresis and various rarely cutting restriction enzymes in single, double and partial digestions, we now report long-range physical maps of the two closest flanking markers, acid phosphatase-1 (Aps-1) and GP79, which span over 400 and 800 kb, respectively. It is concluded that the physical distance between both markers is larger than predicted on the basis of genetic linkage analysis. Furthermore, two RFLP markers (H3F8 and H4H10) which map genetically to the same locus as Aps-1 do not show physical linkage, indicating severe suppression of recombination in this region of the chromosome. Finally, no evidence was obtained showing the presence of a CpG island near Aps-1.